The genetic diversity-productivity effect in wheat cultivar mixtures at multiple levels

There is abundant evidence that biodiversity promotes ecosystem functions in various ecosystems, and recent syntheses stress the need to promote biodiversity in agroecosystems to enhance productivity and stability in a changing climate. Yet, how we can better manipulate genetic biodiversity to achieve these goals in intensive cropping systems is not well understood. Using a large-scale intensive wheat cropping experiment, we studied the effects of wheat genetic diversity on productivity at multiple levels. The results show that the overyielding effects were achieved in mixed cropping at the population, cultivar, and individual levels, which can be considered as a promising way to enhance food security. In addition, wheat cultivar mixtures were temporally more stable than the monocultures. These point to a combination of the positive and negative effects, including complementarity, selection, and competition, in mixtures that affect the cultivars' collective strategies, which are determined by both the complexity of the mixture and the environmental conditions. Furthermore, we found nonmonotonic genetic diversity-productivity relationships that are consistent at multiple levels, suggesting that increasing the number of cultivars in mixed cropping does not always promote productivity. Our results can be directly interpreted for policy and management in ecological cropping systems.